Jessica Winder has a background in ecological studies in both the museum and the research laboratory. She is passionate about the natural world right on our doorsteps. She is enthusiastic about capturing what she sees through photography and wants to open the eyes of everyone to the beauty and fascination of nature.
She is author of 'Jessica's Nature Blog' at http://natureinfocus.wordpress.com.
Jessica has also extensively researched macroscopic variations in oyster and other edible marine mollusc shells from archaeological excavations as a means of understanding past exploitation of marine shellfish resources. She is an archaeo-malacological consultant through Oysters etc. and is publishing summaries of her shell research work on the WordPress Blog called 'Oysters etc.' at http://oystersetcetera.wordpress.com
'Photographic Salmagundi' at http://photosalmagundi.wordpress.com is a showcase of photographs and digital art on all sorts of subjects - not just natural history.
The Silurian rocks at Ferriters Cove are well known for their fossils. I found a few easily recognisable ones as I walked round the cove, such as the brachiopod Leptaena and Favosites coral. The fossils can be seen on the surface of the exposed bedrock and also in the numerous broken pieces of rock that lie on the beach.
Some features I am not sure whether they are fossils or not – they look as if they might be trace fossils – evidence of animal activity in the original sediments rather than the remains of the animal itself. These included some some fairly obvious branching linear features that could conceivably be evidence for crab burrows; each “burrow” is a couple of centimetres wide. The other features are more obscure and much smaller and occur as a pair of parallel curving lines rather like miniature army tank tracks. I thought they might be trace fossils of trilobite tracks. You’ll need to click on the images to view the features close-up and make up your own mind.
The most readily available literature on the Silurian of the Dingle Peninsula does not provide enough details to enable me to understand what has specifically caused the different compositions seen in the sequence of strata in the Dunquin Group at Ferriters Cove (Cuan an Chaoil) itself. I can say though that these sedimentary rocks were deposited approximately 410 million years ago during the Silurian Period in a shallow sea with active volcanoes on its shore and hinterland. The sediments include pale brown, yellow, grey and red mudstones, siltstones and sandstones (frequently very fossiliferous) interbedded with volcanics such as lithic tuffs and lavas.
The sediments were no doubt laid down in this shallow sea in a series of episodes, each reflecting changes in that environment brought about in some part by increase and decrease in depth of the water. The polar ice caps increased and decreased in size during that time resulting in more or less water in the sea, and greater and lesser incursions onto the land. Volcanic ash and fragments would also have periodically rained down on the water and settled to the sea bed.
The photographs in this post show what I think is a particularly attractive group of rock layers. The colours are remarkable – though on another day and in a different light they might not look the same. I wondered if the polygonal pattern was dried cracks in the original soft sediment – but maybe not because the origin of the rock is from sediments laid down in a shallow sea – at this stage I don’t know how feasible an explanation drying out of the sediments by exposure to air would be.
I was only able to investigate a small part of this series of Silurian strata. Greater variations in composition and type are exposed further north along the shoreline in the locality. They include, for example, dark purple porphyritic lava, with large platy phenocrysts with flow alignment – the oldest unit of the Dunquin Group. I would have loved to have seen that. I really will have to go back to Ferriters Cove and discover more of its fascinating geology another time.
The parallel lines of thin strata look like sloping stacks of tombstones in some places on the beach at Ferriters Cove. Rocks at mid to low shore level tend to be superficially darker because of recent wetting, and encrusting biofilms of bacteria, lichen, algae and invertebrate organisms. The dry bare rocks at the top of the shore, however, reveal their true colours. The way that the sharp-edged and angular Silurian sedimentary rock layers project from the sand reminds me of the occasion when my front lawn was covered in broken slate tiles that had embedded themselves in the turf like so many thrown daggers after a violent storm had dislodged them from my roof.
Continuing my geological excursion around Ferriters Cove, the standing height of the jutting strata on the shore increases steadily from ankle height to shin, to knee, and then hip height. It is interesting to note that a few of the exposed rock layers have been eroded in a strange way, maybe because the sediments of which they are composed are softer than the other layers. The weathering of them has resulted in an irregular surface sculpturing, as shown in some of these pictures.
The patterning in this instance is vaguely reminiscent of the large trace fossil burrows that I have previously seen, for example, in Jurassic rocks on the Dorset coast at Winspit and Lyme Regis. I am not sure about these at Ferriters Cove. I think the texture is probably just a reflection of the uneven hardness of the rock. I have found definite “chondrites” fossil burrows in Silurian rocks elsewhere on the Dingle Peninsula at both Smerwick Harbour and Clogher Bay but those trace fossils were distinct and on a much smaller scale.
To continue the investigation of rocks at Ferriters Cove, I followed the curve of the cove to the right (or roughly northwards), where the Silurian strata become higher, exposing their sharp thin edges as they thrust through the beach surface. At high tide level they are bare – no seaweed or encrusting organisms. As the rock layers pass into the base of the low cliff, they retain their steep angle. However, immediately above the bedrock is a thick layer of broken shards lying almost horizontally but with some perturbations; I don’t know how they got like this but wonder if it has something to do with glaciation. This layer of broken pieces is overlain by softer, looser sediments – possibly more geologically recent aeolian or wind-blown accumulations. The clean, dry rocks have pleasing pale green-grey and orange colours.
The wide sandy beach that you see as soon as you get to Ferriters Cove, gives way to a broad expanse of olive green seaweeds at mid tide level that conceals an uneven pavement of low-lying and jagged rocks to which they are attached. These rocks are the first signs of the incredible ancient fossil-bearing Silurian strata for which this cove is famous. Walking around the cove in a northerly direction reveals, one-by-one, a series of strata, each with a character of their own in terms of colour, texture, and shape, and terminating in the massive flat shining slabs of rock that face the cliffs in the distance below Ferriters Castle.
This is the first in a series of posts illustrating the changing nature of the Silurian strata in the sequence exposed at this location.
The wide sandy beach at Ventry lies on the south coast of the Dingle Peninsula in Ireland and is home to a small harbour where boats leave for tours of the Blasket Islands, and it also marks the route of an ancient pilgrims’ way. According to the sign posted in the car park, the Saints’ Road (Cosán na Naomh) starts here in Ventry (Tráigh Fionnetrá) and finishes in Baile Breac at the foot of Mount Brandon over 18 km away. It is today waymarked by the symbol of a monk, and is thought to have been in existence for over a thousand years.
The notice says that “In Old Irish literature, this beach was the scene of a somewhat mythical encounter known as Cath Fionntrá (the battle of Ventry) in which the great hero Fionn Mac Cumhaill overcame the Emperor of all the World except Ireland, Daire Donn”. Now all is calm on the beach with the only sign of struggle being that of the sea against the land. The sand is strewn with pebbles, shells, and sea weed; while the dunes are protected from erosion as in so many other places these days by the placement of large boulders (a structure known as rip-rap).